The process of one computer communicating with another computer at intervals for the purpose of obtaining information or to perform an action is referred to as polling. For example, when a device or service (a client) wants to retrieve data or perform an action on another device or service (a server), the client can poll the server. Polling occurs in many different types of applications including stock price update applications that display current prices for stocks every so often, weather applications that update temperature every so often, and email applications that check for new emails every so often, to mention just a few of many possible applications.
In some polling applications, the client polls the server at some fixed interval or the server sends updates to the client at a fixed interval. Simple optimizations of fixed interval polling can include reducing unnecessary polling. For example, a weather application may detect when a client is idle and stop sending updates until the client becomes active again. A stock price update application may reduce polling frequency after the close of the trading day.